Comments on the existence of circumstellar clouds derived from interstellar Mg observations

From observations of interstellar Mgi, ii resonance lines, Gurzadyan has proposed recently that for the majority of hot stars most of the line-of-sight gas originates in dense, circumstellar clouds. To support this conclusion, which is contrary to most current models of the interstellar gas, he has set out apparently strong theoretical arguments based on empirical evidence from the sample of stars considered. In this paper we have considered the same data and have included some additional observations of interstellar Mg lines. We suggest that an empirical relationship between Mgii equivalent width and stellar effective temperature, which is central to the model proposed by Gurzadyan, may be explained by an observational selection effect. Further, we suggest that while circumstellar material may well contribute in part to observed column densities, there is no firm evidence that most of the gas is located in circumstellar clouds.Based in part on observations by the International Ultraviolet Explorer satellite collected at the Villafranca Tracking Station of the European Space Agency.